There is a charged particle beam apparatus as a technology for measuring a circuit pattern formed on a substrate such as a wafer. The charged particle beam apparatus irradiates one or multiple primary charged particle beam onto a substrate and detects secondary charged particles generated thereby. Then the detected secondary charged particle is imaged onto a display.
In order to quickly process many measurement points on the substrate in the charged particle beam apparatus, it is desirable to reduce time required for example for focus adjustment of the primary charged particle beam to be irradiated onto each measurement point. The focus condition of the primary charged particle beam is determined by the acceleration voltage of the primary charged particle beam, the voltage to be applied to the substrate, and the height of the substrate and the like. For example, the height of the substrate is detected using a reflected light of a laser beam irradiated onto the substrate. The obtained height information is fed back to an optics control system (for example, an objective lens control system) to determine a set parameter of the charged particle optics so that the primary charged particle beam is focused at each measurement point.
In a semiconductor manufacturing process, the charged particle beam apparatus is used for measuring a circuit pattern formed on a wafer, where the wafer may be charged by a process performed before the measurement. For example, the wafer may be charged in resist coating as a material constituting a resist is polarized by friction with a spin coater used therein. Also the wafer may be charged in etching by plasma used therein. When the substrate is charged in the charged particle beam apparatus, an orbit of the primary charged particle beam is disturbed and the beam is not focused at the measurement point, so that the measurement accuracy decreases. International Publication WO 03/007330 discloses a technology for solving this problem.
In the technology described in International Publication WO 03/007330, there is detected a surface potential on a line including a center of a wafer by a charged plate monitor provided in a carrying path into a vacuum chamber, before measurement by a primary charged particle beam. Next, coefficients of a predetermined function are determined by the measurement result of the surface potential to obtain an approximate function representing the surface potential on the line including the wafer center. The wafer has a tendency to be charged in a concentric fashion (rotational symmetry). By taking advantage of this property, an approximate function representing the surface potential distribution over the entire wafer surface is obtained from the approximate function representing the surface potential on the line including the wafer center. The surface potential at a measurement point on the wafer is calculated by the approximate function representing the surface potential distribution over the entire wafer surface. Then a retarding voltage applied to the wafer for adjusting focus of the primary charged particle beam, is corrected by the calculated surface potential. With such a configuration, it is possible to focus the primary charged particle beam at a desired measurement point on the wafer even if the wafer is charged.